Base station apparatus and control channel allocating method

ABSTRACT

A wireless communication base station apparatus that allows the number of times of blind decodings at a mobile station to be reduced without increasing the overhead caused by notifying information. In this apparatus, a CCE allocation part allocates allocation information allocated to a PDCCH received from modulation parts to a particular one of a plurality of search spaces that is corresponding to a CCE aggregation size of the PDCCH. A placement part then places the allocation information in one of downstream line resources, reserved for the PDCCH, that is corresponding to the CCE of the particular search space to which the allocation information has been allocated. A radio transmission part then transmits an OFDM symbol, in which the allocation information has been placed, to the mobile station from an antenna.

The present application is a continuation of U.S. patent applicationSer. No. 14/996,183, filed Jan. 14, 2016, now U.S. Pat. No. 9,380,574,which is a continuation of U.S. patent application Ser. No. 14/842,590,filed Sep. 1, 2015, now U.S. Pat. No. 9,277,550, which is a continuationof U.S. patent application Ser. No. 14/505,429, filed Oct. 2, 2014, nowU.S. Pat. No. 9,161,347, which is a continuation of U.S. patentapplication Ser. No. 14/166,632, filed Jan. 28, 2014, now U.S. Pat. No.8,879,498, which is a continuation of U.S. patent application Ser. No.13/782,940, filed Mar. 1, 2013, now U.S. Pat. No. 8,675,593, which is acontinuation of U.S. patent application Ser. No. 13/354,052, filed Jan.19, 2012, now U.S. Pat. No. 8,411,635, which is a continuation of U.S.patent application Ser. No. 12/847,737, filed Jul. 30, 2010, now U.S.Pat. No. 8,165,085, which is a continuation of U.S. patent applicationSer. No. 12/740,674, filed Apr. 29, 2010, now U.S. Pat. No. 7,920,516,which is a U.S. National-Stage Entry of International Patent ApplicationNo. PCT/JP2008/003067, filed Oct. 28, 2008, which claims the benefit ofJapanese Patent Application No. 2007-280920, filed Oct. 29, 2007. Thedisclosure of Japanese Patent Application No. 2007-280920, filed on Oct.29, 2007, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a radio communication base stationapparatus, radio communication mobile station apparatus and controlchannel allocating method.

BACKGROUND ART

In mobile communication, ARQ (Automatic Repeat reQuest) is applied todownlink data from a radio communication base station apparatus(hereinafter abbreviated to “base station”) to radio communicationmobile station apparatuses (hereinafter abbreviated to “mobilestations”). That is, mobile stations feed back response signalsrepresenting error detection results of downlink data, to the basestation. Mobile stations perform a CRC (Cyclic Redundancy Check) ofdownlink data, and, if CRC=OK is found (i.e. if no error is found), feedback an ACK (ACKnowledgement), or, if CRC=NG is found (i.e. if error isfound), feed back a NACK (Negative ACKnowledgement), as a responsesignal to the base station. These response signals are transmitted tothe base station using uplink control channels such as PUCCHs (PhysicalUplink Control CHannels).

Also, the base station transmits control information for notifyingresource allocation results for downlink data and uplink data, to mobilestations. This control information is transmitted to the mobile stationsusing downlink control channels such as PDCCHs (Physical DownlinkControl CHannels). Each PDCCH occupies one or a plurality of CCEs(Control Channel Elements). The base station generates PDCCHs per mobilestation, allocates CCEs to be occupied by the PDCCHs according to thenumber of CCEs required for control information, maps the controlinformation on the physical resources associated with the allocatedCCEs, and transmits the results.

For example, in order to satisfy desired received quality, an MCS(Modulation and Coding Scheme) of a low MCS level needs to be set for amobile station that is located near the cell boundary where channelquality is poor. Therefore, the base station transmits a PDCCH thatoccupies a larger number of CCEs (e.g. eight CCEs). By contrast, even ifthe MSC of a high MCS level is set for a mobile station that is locatednear the center of a cell where channel quality is good, it is possibleto satisfy desired received quality. Therefore, the base stationtransmits a PDCCH that occupies a smaller number of CCEs (e.g. one CCE).Here, the number of CCEs occupied by one PDCCH is referred to as “CCEaggregation size.”

Also, a base station allocates a plurality of mobile stations to onesubframe and therefore transmits a plurality of PDCCHs at the same time.In this case, the base station transmits control information includingCRC bits scrambled by the mobile station ID numbers of the destination,so that the destination mobile station of each PDCCH can be identified.Further, the mobile stations decode CCEs to which PDCCHs may be mapped,and perform CRC detection after descrambling the CRC bits by the mobilestation ID numbers of those mobile stations. Thus, mobile stationsdetect the PDCCHs for those mobile stations by performing blind decodingof a plurality of PDCCHs included in a received signal.

However, if a larger total number of CCEs are present, the number oftimes a mobile station performs blind decoding increases. Therefore, forthe purpose of reducing the number of times a mobile station performsblind decoding, a method of limiting CCEs targeted for blind decoding ona per mobile station basis is studied (see Non-Patent Document 1). Withthis method, a plurality of mobile stations are grouped, and CCE fieldsbeing CCEs targeted for blind decoding are limited on a per group basis.By this means, the mobile station of each group needs to perform blinddecoding of only the CCE field allocated to that mobile station, so thatit is possible to reduce the number of times of blind decoding. Here,the CCE field targeted for blind decoding by a mobile station isreferred to as “search space.”

Also, to use downlink communication resources efficiently withoutsignaling to notify PUCCHs for transmitting response signals, from thebase station to the mobile stations for transmitting response signals,studies are underway to associate CCEs and PUCCHs on a one-to-one basis(see Non-Patent Document 2). According to this association, each mobilestation can decide the PUCCH to use to transmit a response signal fromthat mobile station, from the CCE associated with the physical resourceon which control information for that mobile station is mapped.Therefore, each mobile station maps a response signal from that mobilestation on a physical resource, based on the CCE associated with thephysical resource on which control information for that mobile stationis mapped.

-   Non-Patent Document 1: 3GPP RAN WG1 Meeting document, R1-073996,    “Search Space definition: Reduced PDCCH blind detection for split    PDCCH search space”, Motorola-   Non-Patent Document 2: 3GPP RAN WG1 Meeting document, R1-073620,    “Clarification of Implicit Resource Allocation of Uplink ACK/NACK    Signal”, Panasonic.

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, if a plurality of mobile stations are grouped and search spacesare set on a per group basis, a base station needs to notify searchspace information indicating the search space of each mobile station, toeach mobile station. Therefore, in the above conventional technique, theoverhead increases due to notification information.

It is therefore an object of the present invention to provide a radiocommunication base station apparatus, radio communication mobile stationapparatus and control channel allocating method for reducing the numberof times a mobile station performs blind decoding, without increasingthe overhead due to notification information.

Means for Solving the Problem

The radio communication base station apparatus employs a configurationhaving: an allocating section that allocates a control channel thatoccupies one or a plurality of control channel elements to a specificcontrol channel element field matching a number of control channelelements occupied by the control channel, among a plurality of controlchannel element fields; and a transmitting section that transmits thecontrol channel allocated to the specific control channel element field.

Advantageous Effect of the Invention

According to the present invention, it is possible to reduce the numberof times a mobile station performs blind decoding, without increasingthe overhead due to notification information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 2 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 1 of the present invention;

FIG. 3 shows search space information according to Embodiment 1 of thepresent invention;

FIG. 4 shows search spaces according to Embodiment 1 of the presentinvention;

FIG. 5 shows an example of CCE allocation according to Embodiment 1 ofthe present invention;

FIG. 6 shows search space information according to Embodiment 1 of thepresent invention (in the case where the cell size is large);

FIG. 7 shows search spaces according to Embodiment 1 of the presentinvention (in the case where the cell size is large);

FIG. 8 shows search spaces according to Embodiment 2 of the presentinvention;

FIG. 9 shows search spaces according to Embodiment 3 of the presentinvention (in allocating method 1);

FIG. 10 shows search spaces according to Embodiment 3 of the presentinvention (in allocating method 2);

FIG. 11 shows search spaces according to Embodiment 4 of the presentinvention (CFI=3);

FIG. 12 shows search spaces according to Embodiment 4 of the presentinvention (CFI=2);

FIG. 13 shows search spaces according to Embodiment 4 of the presentinvention (CFI=1);

FIG. 14 shows the priority order relating to a use of physical resourcesassociated with PUCCHs according to Embodiment 5 of the presentinvention;

FIG. 15 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=3);

FIG. 16 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=2);

FIG. 17 shows PUCCH resources according to Embodiment 5 of the presentinvention (CFI=1);

FIG. 18 shows other search spaces (example 1); and

FIG. 19 shows other search spaces (FIG. 2).

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings. In the followingexplanation, assume that the total number of CCEs allocated to a PDCCHis 32, from CCE #0 to CCE #31, and the PDCCH CCE aggregation size is oneof 1, 2, 4 and 8. Also, if one PDCCH occupies a plurality of CCEs, theplurality of CCEs occupied by the PDCCH are consecutive.

Also, a case will be explained with the following explanation, where ZAC(Zero Auto Correlation) sequences are used in the first spreading ofPUCCHs and block-wise spreading code sequences, which are used inspreading in LB (Long Block) units, are used in second spreading.However, in the first spreading, it is equally possible to use sequencesthat can be separated from each other by different cyclic shift values,other than ZAC sequences. For example, in the first spreading, it isequally possible to use GCL (Generalized Chirp Like) sequences, CAZAC(Constant Amplitude Zero Auto Correlation) sequences, ZC (Zadoff-Chu)sequences, or use PN sequences such as M sequences and orthogonal Goldcode sequences. Also, in second spreading, as block-wise spreading codesequences, it is possible to use any sequences that can be regarded asorthogonal sequences or substantially orthogonal sequences. For example,in second spreading, it is possible to use Walsh sequences or Fouriersequences as block-wise spreading code sequences.

Also, in the following explanation, assume that the CCE numbers and thePUCCH numbers are associated. That is, the PUCCH number is derived fromthe CCE number used for a PDCCH to use to allocate uplink data.

Embodiment 1

FIG. 1 shows the configuration of base station 100 according to thepresent embodiment, and FIG. 2 shows the configuration of mobile station200 according to the present embodiment.

Here, to avoid complicated explanation, FIG. 1 shows componentsassociated with transmission of downlink data and components associatedwith reception of uplink response signals to downlink data, which areclosely related to the present invention, and the illustration andexplanation of the components associated with reception of uplink datawill be omitted. Similarly, FIG. 2 shows components associated withreception of downlink data and components associated with transmissionof uplink response signals to downlink data, which are closely relatedto the present invention, and the illustration and explanation of thecomponents associated with transmission of uplink data will be omitted.

In base station 100 shown in FIG. 1, encoding section 101 receives asinput search space information indicating the definition of a searchspace determined by, for example, the cell size and base stationenvironment. Further, encoding section 101 encodes the search spaceinformation received as input, and outputs the result to modulatingsection 102. Next, modulating section 102 modulates the encoded searchspace information received as input from encoding section 101, andoutputs the result to mapping section 108.

Encoding and modulating sections 103-1 to 103-K receive as inputresource allocation information for uplink data or downlink datadirected to mobile stations. Here, each allocation information isallocated to a PDCCH of the CCE aggregation size required to transmitthat allocation information. Further, encoding and modulating sections103-1 to 103-K are provided in association with maximum K mobilestations #1 to #K. In encoding and modulating sections 103-1 to 103-K,encoding sections 11 each encode allocation information received asinput and allocated to PDCCHs, and output the results to modulatingsections 12. Next, modulating sections 12 each modulate the encodedallocation information received as input from encoding sections 11, andoutput the results to CCE allocating section 104.

CCE allocating section 104 allocates the allocation information receivedas input from modulating sections 103-1 to 103-K, to one or a pluralityof CCEs based on search space information. To be more specific, CCEallocating section 104 allocates a PDCCH to a specific search spaceassociated with the CCE aggregation size of that PDCCH, among aplurality of search spaces. Further, CCE allocating section 104 outputsallocation information allocated to CCEs, to mapping section 108. Here,the CCE allocating method in CCE allocating section 104 will bedescribed later.

On the other hand, encoding section 105 encodes transmission data (i.e.downlink data) received as input and outputs the result toretransmission control section 106. Here, if there are a plurality itemsof transmission data for a plurality of mobile stations, encodingsection 105 encodes each of the plurality items of transmission data forthese mobile stations.

Upon the initial transmission, retransmission control section 106 holdsand outputs encoded transmission data of each mobile station tomodulating section 107. Here, retransmission control section 106 holdstransmission data until an ACK from each mobile station is received asinput from deciding section 117. Further, if a NACK from each mobilestation is received as input from deciding section 117, that is, uponretransmission, retransmission control section 106 outputs transmissiondata associated with that NACK to modulating section 107.

Modulating section 107 modulates encoded transmission data received asinput from retransmission control section 106, and outputs the result tomapping section 108.

Mapping section 108 maps allocation information to downlink allocationresources associated with the allocated CCEs among downlink resourcesreserved for PDCCHs, maps search space information to downlink resourcesreserved for broadcast channels, and maps transmission data to downlinkresources reserved for transmission data. Further, mapping section 108outputs signals to which those channels are mapped, to IFFT (InverseFast Fourier Transform) section 109.

IFFT section 109 generates an OFDM symbol by performing an IFFT of aplurality of subcarriers to which allocation information, search spaceinformation and transmission data are mapped, and outputs the result toCP (Cyclic Prefix) attaching section 110.

CP attaching section 110 attaches the same signal as the signal at thetail end part of the OFDM symbol, to the head of that OFDM symbol, as aCP.

Radio transmitting section 111 performs transmission processing such asD/A conversion, amplification and up-conversion on the OFDM symbol witha CP, and transmits the result from antenna 112 to mobile station 200(in FIG. 2).

On the other hand, radio receiving section 113 receives a SC-FDMA(Single-Carrier Frequency Division Multiple Access) symbol transmittedfrom each mobile station, via antenna 112, and performs receivingprocessing such as down-conversion and A/D conversion on this SC-FDMAsymbol.

CP removing section 114 removes the CP attached to the SC-FDMA symbolsubjected to receiving processing.

Despreading section 115 despreads the response signal by the block-wisespreading code sequence used in second spreading in mobile station 200,and outputs the despread response signal to correlation processingsection 116.

Correlation processing section 116 finds the correlation value betweenthe despread response signal and the ZAC sequence that is used in thefirst spreading in mobile station 200, and outputs the correlation valueto deciding section 117.

Deciding section 117 detects response signals on a per mobile stationbasis, by detecting the correlation peaks in the detection windows on aper mobile station basis. For example, upon detecting the correlationpeak in detection window #0 for mobile station #0, deciding section 117detects the response signal from mobile station #0. Further, decidingsection 117 decides whether the detected response signal is an ACK orNACK, by synchronization detection using the correlation value of areference signal, and outputs the ACK or NACK to retransmission controlsection 106 on a per mobile station basis.

On the other hand, mobile station 200 shown in FIG. 2 receives searchspace information, allocation information and downlink data transmittedfrom base station 100. The methods of receiving these items ofinformation will be explained below.

In mobile station 200 shown in FIG. 2, radio receiving section 202receives an OFDM symbol transmitted from base station 100 (in FIG. 1),via antenna 201, and performs receiving processing such asdown-conversion and A/D conversion on the OFDM symbol.

CP removing section 203 removes the CP attached to the OFDM symbolsubjected to receiving processing.

FFT (Fast Fourier Transform) section 204 acquires allocationinformation, downlink data and broadcast information including searchspace information, which are mapped on a plurality of subcarriers, byperforming an FFT of the OFDM symbol, and outputs the results toseparating section 205.

Separating section 205 separates broadcast information mapped toresources reserved in advance for broadcast channels, from signalsreceived as input from FFT section 204, and outputs the broadcastinformation to broadcast information decoding section 206 andinformation other than the broadcast information to extracting section207.

Broadcast decoding section 206 decodes the broadcast informationreceived as input from separating section 205 to acquire search spaceinformation, and outputs the search space information to extractingsection 207.

Assume that extracting section 207 and decoding section 209 receive inadvance coding rate information indicating the coding rate of allocationinformation, that is, information indicating the PDCCH CCE aggregationsize.

Also, upon receiving allocation information, extracting section 207extracts allocation information from the plurality of subcarriersaccording to the CCE aggregation size and search space informationreceived as input, and outputs the allocation information todemodulating section 208.

Demodulating section 208 demodulates the allocation information andoutputs the result to decoding section 209.

Decoding section 209 decodes the allocation information according to theCCE aggregation size received as input, and outputs the result todeciding section 210.

On the other hand, upon receiving downlink data, extracting section 207extracts downlink data for the subject mobile station from the pluralityof subcarriers, according to the resource allocation result received asinput from deciding section 210, and outputs the downlink data todemodulating section 212. This downlink data is demodulated indemodulating section 212, decoded in decoding section 213 and receivedas input in CRC section 214.

CRC section 214 performs an error detection of the decoded downlink datausing CRC, generates an ACK in the case of CRC=OK (no error) or a NACKin the case of CRC=NG (error present), as a response signal, and outputsthe generated response signal to modulating section 215. Further, in thecase of CRC=OK (no error), CRC section 214 outputs the decoded downlinkdata as received data.

Deciding section 210 performs a blind detection as to whether or not theallocation information received as input from decoding section 209 isdirected to the subject mobile station. To be more specific, against theallocation information received as input from decoding section 209,deciding section 210 performs a blind detection as to whether or not theallocation information is directed to the subject mobile station. Forexample, deciding section 210 decides that, if CRC=OK is found (i.e. noerror is found) as a result of demasking CRC bits by the ID number ofthe subject mobile station, allocation information is directed to thatmobile station. Further, deciding section 210 outputs the allocationinformation directed to the subject mobile station, that is, theresource allocation result of downlink data for that mobile station, toextracting section 207.

Further, deciding section 210 decides a PUCCH that is used to transmit aresponse signal from the subject mobile station, from the CCE numberassociated with a subcarrier to which a PDCCH is mapped, where theallocation information directed to that mobile station is allocated tothat PDCCH. Further, deciding section 210 outputs the decision result(i.e. PUCCH number) to control section 209. For example, if a CCEassociated with a subcarrier to which PDCCH directed to the subjectmobile station is mapped is CCE #0, deciding section 210 decides thatPUCCH #0 associated with CCE #0 is the PUCCH for that mobile station.Also, for example, if CCEs associated with subcarriers to which PDCCHdirected to the subject mobile station is mapped are CCE #0 to CCE #3,deciding section 210 decides that PUCCH #0 associated with CCE #0 of theminimum number among CCE #0 to CCE #3, is the PUCCH for that mobilestation.

Based on the PUCCH number received as input from deciding section 210,control section 211 controls the cyclic shift value of the ZAC sequenceused in the first spreading in spreading section 216 and the block-wisespreading code sequence used in second spreading in spreading section219. For example, control section 211 selects the ZAC sequence of thecyclic shift value associated with the PUCCH number received as inputfrom deciding section 210, among twelve ZAC sequences from ZAC #0 to ZAC#11, and sets the ZAC sequence in spreading section 216, and selects theblock-wise spreading code sequence associated with the PUCCH numberreceived as input from deciding section 210, among three block-wisespreading code sequences from BW #0 to BW #2, and sets the block-wisespreading code sequence in spreading section 219. That is, controlsection 211 selects one of the plurality of resources defined by ZAC #0to ZAC #11 and by BW #0 to BW #2.

Modulating section 215 modulates the response signal received as inputfrom CRC section 214 and outputs the result to spreading section 216.

Spreading section 216 performs first spreading of the response signal bythe ZAC sequence set in control section 211, and outputs the responsesignal subjected to the first spreading to IFFT section 217. That is,spreading section 216 performs first spreading of the response signalusing the ZAC sequence of the cyclic shift value associated with theresource selected in control section 211.

IFFT section 217 performs an IFFT of the response signal subjected tothe first spreading, and outputs the response signal subjected to anIFFT to CP attaching section 218.

CP attaching section 218 attaches the same signal as the tail end partof the response signal subjected to an IFFT, to the head of thatresponse signal as a CP.

Spreading section 219 performs second spreading of the response signalwith a CP by the block-wise spreading code sequence set in controlsection 211, and outputs the response signal subjected to secondspreading to radio transmitting section 220.

Radio transmitting section 220 performs transmission processing such asD/A conversion, amplification and up-conversion on the response signalsubjected to second spreading, and transmits the result from antenna 201to base station 100 (in FIG. 1).

Next, the CCE allocating method in CCE allocating section 104 will beexplained in detail.

CCE allocating section 104 allocates PDCCHs directed to mobile stations,to a search space associated with the CCE aggregation size of thosePDCCHs to which allocation information for those mobile stations isallocated, among a plurality of search spaces.

Here, as shown in FIG. 3, CCE allocating section 104 receives as inputsearch space information defining the CCE numbers representing thestarting locations of search spaces and the numbers of CCEs representingthe search space lengths, on a per CCE aggregation size basis. Forexample, the search space associated with a CCE aggregation size of 1 isdefined where the CCE number representing the starting location is CCE#0 and the number of CCEs is 10. Similarly, the search space associatedwith a CCE aggregation size of 2 is defined where the CCE numberrepresenting the starting location is CCE #4 and the number of CCEs is12. The same applies to the case where the CCE aggregation size is 4 or8.

Therefore, as shown in FIG. 4, a search space formed with ten CCEs fromCCE #0 to CCE #9 is defined when the CCE aggregation size is 1, a searchspace formed with twelve CCEs from CCE #4 to CCE #15 is defined when theCCE aggregation size is 2, a search space formed with sixteen CCEs fromCCE #8 to CCE #23 is defined when the CCE aggregation size is 3, and asearch space formed with sixteen CCEs from CCE #16 to CCE #31 is definedwhen the CCE aggregation size is 4.

That is, as shown in FIG. 4, CCE allocating section 104 can allocatemaximum ten PDCCHs of a CCE aggregation size of 1 to the search space ofCCE #0 to CCE #9. Similarly, CCE allocating section 104 can allocatemaximum six PDCCHs of a CCE aggregation size of 2 to the search space ofCCE #4 to CCE #15, allocate maximum four PDCCHs of a CCE aggregationsize of 4 to the search space of CCE #8 to CCE #23, and allocate maximumtwo PDCCHs of a CCE aggregation size of 8 to the search space of CCE #16to CCE #31.

For example, a case will be explained where CCE allocating section 104of base station 100 allocates six PDCCH's of a CCE aggregation size of1, three PDCCHs of a CCE aggregation size of 2, three PDCCHs of a CCEaggregation size of 4 and one PDCCH of a CCE aggregation size of 8.

First, as shown in FIG. 5, CCE allocating section 104 allocates sixPDCCH's (of a CCE aggregation size of 1) to CCE #0 to CCE #5 in thesearch space (CCE #0 to CCE #9) associated with a CCE aggregation sizeof 1 shown in FIG. 4. Next, as shown in FIG. 5, CCE allocating section104 allocates three PDCCHs (of a CCE aggregation size of 2) to CCEs #6and #7, CCEs #8 and #9 and CCEs #10 and #11, to which PDCCHs of a CCEaggregation size of 1 are not allocated, in the search space (CCE #4 toCCE #15) associated with a CCE aggregation size of 2 shown in FIG. 4.Further, as shown in FIG. 5, CCE allocating section 104 allocates threePDCCHs (of a CCE aggregation size of 4) to CCEs #12 to #15, CCEs #16 to#19 and CCEs #20 to #23, to which PDCCHs of CCE aggregation sizes of 1and 2 are not allocated, in the search space (CCE #8 to CCE #23)associated with a CCE aggregation size of 4 shown in FIG. 4. Further, asshown in FIG. 5, CCE allocating section 104 allocates one PDCCH (of aCCE aggregation size of 8) to CCEs #24 to #31, to which PDCCHs of CCEaggregation sizes of 1, 2 and 4 are not allocated, in the search space(CCE #16 to CCE #31) associated with a CCE aggregation size of 8 shownin FIG. 4.

Mobile station 200 performs demodulation, decoding and blind detectionof PDCCHs using the definition of search spaces based on the CCEaggregation sizes. By this means, it is possible to reduce the number oftimes of blind detection in demodulating section 208, decoding section209 and deciding section 210 of mobile station 200 (in FIG. 2). To bemore specific, if blind detection is performed presuming that the CCEaggregation size is 1, extracting section 207 outputs only signalsassociated with CCE #0 to CCE #9 to demodulating section 208 among CCE#0 to CCE #31 shown in FIG. 4. That is, in demodulating section 208,decoding section 209 and deciding section 210, when a CCE aggregationsize is 1, the target of blind detection is limited to the search spacesupporting CCE #0 to CCE #9. Similarly, if blind detection is performedwhen the CCE aggregation size is 2, extracting section 207 outputs onlysignals associated with CCE #4 to CCE #15 to demodulating section 208among CCE #0 to CCE #31 shown in FIG. 4. The same applies to the casewhere the CCE aggregation size presumes 4 or 8.

Thus, each mobile station performs blind decoding using search spacesassociated with the CCE aggregation sizes. That is, by defining onesearch space information per cell, mobile stations can perform blinddecoding unless a base station notifies search space information tothese mobile stations.

Here, to reduce degradation of error rate performance of allocationinformation, the MCS of allocation information directed to mobilestations that are located near a cell edge is set lower. Therefore, thePDCCH CCE aggregation size for mobile stations that are located near acell edge increases. For example, out of the CCE aggregation sizes 1, 2,4 and 8, the CCE aggregation size for mobile stations that are locatednear a cell edge is 4 or 8.

Also, in a cell of a larger cell size, the proportion of mobile stationsrequiring transmission of allocation information with a low MCS set,that is, the proportion of mobile stations, to which PDCCHs of a largerCCE aggregation size are allocated, increases. In other words, in a cellof a smaller cell size, the proportion of mobile stations that cantransmit allocation information with a high MCS set, that is, theproportion of mobile stations, to which PDCCHs of a smaller CCEaggregation size are allocated, increases.

Therefore, a base station defines search spaces that vary between cellsizes. That is, in a larger cell size, a wider search space is definedfor a larger CCE aggregation size, and a narrower search space isdefined for a smaller CCE aggregation size. Also, in a smaller cellsize, a narrower search space is defined for a larger CCE aggregationsize, and a wider search space is defined for a smaller CCE aggregationsize.

Also, CCE allocating section 104 allocates control information to aspecific search space among a plurality of search spaces defined percell.

For example, FIG. 6 shows an example of search space information in acell of a larger cell size than a cell in which the search spaceinformation shown in FIG. 3 is set. To be more specific, the searchspace associated with a CCE aggregation size of 1 is defined where theCCE number representing the starting location is CCE #0 and the numberof CCEs is 6. Similarly, the search space associated with a CCEaggregation size of 2 is defined where the CCE number representing thestarting location is CCE #2 and the number of CCEs is 8. The sameapplies to the case where the CCE aggregation size is 4 or 8.

That is, as shown in FIG. 7, CCE allocating section 104 can allocatemaximum six PDCCHs of a CCE aggregation size of 1 to the search space ofCCE #0 to CCE #5. Similarly, CCE allocating section 104 can allocatemaximum four PDCCHs of a CCE aggregation size of 2 to the search spaceof CCE #2 to CCE #9, allocate maximum five PDCCHs of a CCE aggregationsize of 4 to the search space of CCE #4 to CCE #23, and allocate maximumthree PDCCHs of a CCE aggregation size of 8 to the search space of CCE#8 to CCE #31.

Here, if the search spaces shown in FIG. 7 are compared to the searchspaces shown in FIG. 4, in a smaller CCE aggregation size, that is, in aCCE aggregation size of 1 (or a CCE aggregation size of 2), the numberof PDCCHs allocated decreases from 10 (6) to 6 (4). By contrast, in alarger CCE aggregation size, that is, in a CCE aggregation size of 4 (ora CCE aggregation size of 8), the number of PDCCHs allocated increasesfrom 4 (2) to 5 (3). That is, in CCE allocating section 104, the numberof PDCCHs of a larger CCE aggregation size increases in a larger cellsize, so that it is possible to allocate more PDCCHs of a larger CCEaggregation size. In other words, in CCE allocating section 104, thenumber of PDCCHs of a smaller CCE aggregation size increases in asmaller cell size, so that it is possible to allocate more PDCCHs of asmaller CCE aggregation size.

Thus, according to the present embodiment, only search spaces that aredefined per cell are the target of blind decoding in a mobile station,so that it is possible to reduce the number of times to perform blinddecoding. Also, mobile stations specify search spaces based on searchspace information broadcasted for all the mobile stations from a basestation, so that new notification information per mobile station is notrequired. Therefore, according to the present embodiment, it is possibleto reduce the number of times of blind decoding, without increasing theoverhead due to notification information.

Further, according to the present embodiment, PDCCHs are allocated to asearch space associated with the CCE aggregation size. By this means, ina plurality of CCEs, the CCE aggregation size of PDCCHs for use islimited. Therefore, according to the present embodiment, by associatingPUCCHs with only CCEs of the minimum numbers among the CCEs formingPDCCHs for use, it is possible to reduce the amount of resourcesreserved for PUCCHs.

Also, a case has been described above with the present embodiment wherePDCCHs of all CCE aggregation sizes can be transmitted to a certainmobile station. However, with the present invention, it is equallypossible to determine the CCE aggregation size per mobile station. Forexample, for a mobile station that is located near a cell edge, channelquality is poor, and, consequently, the ratio of transmission with alower MCS increases. Therefore, the CCE aggregation size in a mobilestation that is located near a cell edge is limited to 4 or 8. Also, fora mobile station that is located near a cell center, channel quality isgood, and, consequently, the ratio of transmission with a higher MCSincreases. Therefore, the CCE aggregation size of a mobile station thatis located near a cell center is limited to 1 or 2. By this means, it iseasier to further specify a search space, so that it is possible tofurther reduce the number of times a mobile station performs blinddecoding.

Also, although a case has been described above with the presentembodiment where the definition of search spaces is set based on thecell size, with the present invention, it is equally possible to set thedefinition of search spaces based on, for example, the bias ofdistribution of mobile stations in a cell.

Embodiment 2

In the search spaces shown in FIG. 4 of Embodiment 1, if an odd numberof PDCCHs of a given CCE aggregation size are used, a CCE may arisewhich cannot be used as a PDCCH of a larger CCE aggregation size thanthe given CCE aggregation size.

For example, in the search spaces shown in FIG. 4, if five PDCCHs of aCCE aggregation size of 1 are used, CCE #0 to CCE #4 are occupied. Inthis case, out of PDCCHs of a CCE aggregation size of 2, the PDCCHformed with CCE #4 and CCE #5 cannot be used because CCE #4 is alreadyused. That is, CCE #5 is not used. Similarly, for example, if threePDCCHs of a CCE aggregation size of 4 are used, CCE #8 to CCE #19 areoccupied. In this case, out of PDCCHs of a CCE aggregation size of 8,the PDCCH formed with CCE #16 to CCE #23 cannot be used because CCE #16to CCE #19 are already used. That is, CCE #20 to CCE #23 are not used.Thus, a part of CCEs forming a PDCCH is used by another PDCCH of adifferent CCE aggregation size, and, consequently, the use efficiency ofCCEs becomes poor.

Therefore, according to the present embodiment, allocation informationis allocated to a specific search space formed with CCEs of lower CCEnumbers in a larger CCE aggregation size.

To be more specific, as shown in FIG. 8, a search space formed withsixteen CCEs from CCE #0 to CCE #15 is defined when the CCE aggregationsize is 8, a search space formed with sixteen CCEs from CCE #8 to CCE#23 is defined when the CCE aggregation size is 4, a search space formedwith twelve CCEs from CCE #16 to CCE #27 is defined when the CCEaggregation size is 2, and a search space formed with ten CCEs from CCE#22 to CCE #31 is defined when the CCE aggregation size is 1.

Here, a case will be explained where CCE allocating section 104 of basestation 100 allocates five PDCCHs of a CCE aggregation size of 1, threePDCCHs of a CCE aggregation size of 2, two PDCCHs of a CCE aggregationsize of 4 and one PDCCH of a CCE aggregation size of 8.

First, as shown in FIG. 8, CCE allocating section 104 allocates onePDCCH (of a CCE aggregation size of 8) to CCE #0 to CCE #7 in the searchspace (CCE #0 to CCE #15) associated with a CCE aggregation size of 8.Next, as shown in FIG. 8, CCE allocating section 104 allocates twoPDCCHs (of a CCE aggregation size of 4) to CCEs #8 to #11 and CCEs #12to #15, to which a PDCCH of a CCE aggregation size of 8 is notallocated, in the search space (CCE #8 to CCE #23) associated with a CCEaggregation size of 4. Further, as shown in FIG. 8, CCE allocatingsection 104 allocates three PDCCHs (of a CCE aggregation size of 2) toCCEs #16 and #17, CCEs #18 and #19 and CCEs #20 and #21, to which PDCCHsof CCE aggregation sizes of 8 and 4 are not allocated, in the searchspace (CCE #16 to CCE #27) associated with a CCE aggregation size of 2.Further, as shown in FIG. 8, CCE allocating section 104 allocates fivePDCCHs (of a CCE aggregation size of 1) to CCEs #22 to #26 in the searchspace (CCE #16 to CCE #31) associated with a CCE aggregation size of 1.Also, different CCEs from the CCEs used for PDCCHs, that is, unused CCEsare concentrated in CCE numbers (i.e. CCE #27 to CCE #31) near the tailend among CCE #0 to CCE #31.

That is, in CCE allocating section 104, if a plurality of PDCCHs ofdifferent CCE aggregation sizes are allocated, it is possible toallocate a plurality of PDCCHs to a plurality of consecutive CCEswithout causing unused CCEs. By this means, in each CCE, CCEs are usedin order from the CCE of the lowest CCE number, and, if unused CCEsoccur, these unused CCEs are likely to be concentrated in CCE numbersnear the tail end.

Thus, if CCEs of lower CCE numbers are used in order from PDCCHs of thelargest CCE aggregation size, CCE allocating section 104 can allocatePDCCHs of a different CCE aggregation size in order from the CCEimmediately after the CCEs to which PDCCHs of a larger CCE aggregationsize are allocated. Therefore, unlike Embodiment 1, it is possible toprevent CCEs from being unavailable because PDCCHs of a different CCEaggregation size are already allocated to these CCEs, so that it ispossible to allocate PDCCHs efficiently. Also, unused CCEs areconcentrated in CCE numbers near the tail end, and, consequently, forexample, a base station reduces and transmits the number of CCEs towhich PDCCHs are actually allocated (in the above example, CCEs arereduced to 27) and which are transmitted, so that it is possible to useavailable resources (in the above example, five CCEs from CCE #27 to CCE#31) efficiently as data resources. Also, even if unused CCEs arepresent in locations other than the locations of CCE numbers near thetail end, although a base station can reduce the number of CCEs to whichPDCCHs are allocated and which are transmitted, an enormous amount ofcontrol information is necessary to notify which CCE is unused. However,as in the present embodiment, when unused CCEs are concentrated in CCEnumbers near the tail end, only the number of CCEs for transmissionneeds to be notified, so that only a small amount of control informationis required.

Thus, according to the present embodiment, allocation information isallocated to a specific search space formed with CCEs of lower CCEnumbers in a larger CCE aggregation size. By this means, it is possibleto allocate PDCCHs in order from the CCE of the lowest CCE numberwithout causing unused CCEs, and gather unused CCEs in consecutive CCEsof CCE numbers near the tail end. Therefore, according to the presentembodiment, it is possible to allocate PDCCHs to CCEs more efficientlythan in Embodiment 1 and use unused CCEs efficiently as data resources.

Embodiment 3

A case will be explained with the present embodiment where downlinkallocation information and uplink allocation information share aplurality of CCEs.

The method of allocating CCEs in the present embodiment will beexplained.

<Allocating Method 1>

With the present embodiment, in a plurality of CCEs forming a specificsearch space, downlink allocation information for notifying a downlinkallocation result is allocated in ascending order from the CCE of thelowest CCE number, and uplink allocation information for notifying anuplink allocation result is allocated in descending order from the CCEof the highest CCE number.

This will be explained below in detail. Here, the same search spaces asthose in FIG. 8 of Embodiment 2 will be used. Also, the above will beexplained focusing on the case where the CCE aggregation size is 1.

As shown in FIG. 9, in the search space (CCEs #22 to #31) matching a CCEaggregation size of 1, CCE allocating section 104 allocates downlinkallocation information (of a CCE aggregation size of 1) in ascendingorder from CCE #22, which is the CCE of the lowest CCE number. That is,CCE allocating section 104 allocates downlink allocation information inorder from CCE #22 to CCE #31. By contrast, as shown in FIG. 9, in thesearch space (CCEs #22 to #31) matching a CCE aggregation size of 1, CCEallocating section 104 allocates uplink allocation information (of a CCEaggregation size of 1) in descending order from CCE #31, which is theCCE of the highest CCE number. That is, CCE allocating section 104allocates downlink allocation information in order from CCE #31 to CCE#22. The same applies to CCE aggregation sizes of 2, 4 and 8.

In CCE #22 to CCE #31 shown in FIG. 9, CCE #22 is used most frequentlyas a PDCCH for downlink allocation information, and CCE #31 is used mostfrequently as a PDCCH for uplink allocation information. In other words,CCE #22 is used least frequently as a PDCCH for uplink allocationinformation. That is, in CCE #22 to CCE #31 shown in FIG. 9, CCE #22,which is used least frequently as a PDCCH for uplink allocationinformation, is used as a PDCCH for downlink allocation, and CCE #31,which is used least frequently as a PDCCH for downlink allocationinformation, is used as a PDCCH for uplink allocation information.

Thus, with the present allocating method, even if downlink allocationinformation and uplink allocation information share a plurality of CCEs,it is possible to acquire the same effect as in Embodiment 2 and use theplurality of CCEs efficiently between downlink allocation informationand uplink allocation information.

Further, a plurality of items of downlink allocation information or aplurality of items of uplink allocation information are not transmittedto a mobile station. Consequently, when a mobile station decidesdownlink allocation information, by performing blind detection in orderfrom the CCE of the lowest CCE number and stopping blind detection ofdownlink allocation information at the time the PDCCH for that mobilestation is found, it is possible to reduce an average number of times ofblind detection, compared to a case where uplink allocation informationand downlink allocation information are mapped in a random manner.Therefore, according to the present embodiment, it is possible to reducethe power consumption in mobile stations.

<Allocating Method 2>

With the present allocating method, allocation information is allocatedto a search space which is formed symmetrically with CCEs of lower CCEnumbers and CCEs of higher CCE numbers in the case of a larger CCEaggregation size.

This will be explained below in detail. As shown in FIG. 10, searchspaces formed with eight CCEs from CCE #0 to CCE #7 and eight CCEs fromCCE #24 to CCE #31 are defined when the CCE aggregation size is 8,search spaces formed with eight CCEs from CCE #4 to CCE #11 and eightCCEs from CCE #20 to CCE #27 are defined when the CCE aggregation sizeis 4, search spaces formed with six CCEs from CCE #8 to CCE #13 and sixCCEs from CCE #18 to CCE #23 are defined when the CCE aggregation sizeis 2, and a search space formed with eight CCEs from CCE #12 to CCE #19is defined when the CCE aggregation size is 1.

That is, each search space is formed with CCEs symmetrically withreference to the center of CCE #0 to CCE #31 (i.e. between CCE #15 andCCE #16).

Also, as shown in FIG. 10, in the same way as in allocating method 1,CCE allocating section 104 allocates downlink allocation information inascending order from the CCE of the lowest CCE number in each searchspace, and allocates uplink allocation information in descending orderfrom the CCE of the highest CCE number in each search space. That is, inCCE #0 to CCE #31 shown in FIG. 10, while the search space (CCE #0 toCCE #15) formed with CCEs of lower CCE numbers than the center of allCCEs is used more frequently as PDCCHs for downlink allocationinformation, the search space (CCE #16 to CCE #31) formed with CCEs ofhigher CCE numbers than the center of all CCEs is used more frequentlyas PDCCHs for uplink allocation information.

Thus, according to the present allocating method, compared to allocatingmethod 1, it is possible to allocate downlink allocation information anduplink allocation information of different CCE aggregation sizesseparately, so that it is possible to perform scheduling more easily tooptimize allocation of CCEs for downlink allocation information and CCEsfor uplink allocation information.

The methods of allocating CCEs have been described above.

Thus, according to the present embodiment, even if downlink allocationinformation and uplink allocation information share a plurality of CCEs,it is possible to reduce the number of times of blind decoding withoutincreasing the overhead due to notification information.

Also, according to the present embodiment, it is possible to acquire thesame effect as above by allocating uplink allocation information inascending order from the CCE of the lowest CCE number and allocatingdownlink allocation information in descending order from the CCE of thehighest CCE number among a plurality of CCEs forming a specific searchspace.

Embodiment 4

With the present embodiment, the allocation information is allocated toa specific search space shifted based on the CFI (Control FormatIndicator) value.

CFI, which is information indicating the amount of PDCCH resources, isnotified from a base station to mobile stations. To be more specific,the CFI value (=3, 2, 1) is associated with the number of OFDM symbolsincluding allocation information. Here, while the above search spaceinformation is broadcasted semi-statically from the base station to themobile stations, CFI is notified dynamically from the base station tothe mobile stations on a per subframe basis. That is, OFDM symbolsincluding allocation information vary between subframes dynamically.Consequently, if the definition of search spaces is set based on thenumber of OFDM symbols including allocation information, that is, basedon the total number of CCEs, it is necessary to notify search spaceinformation from the base station to the mobile stations every time CFIvaries, and therefore the overhead due to notification informationincreases.

Therefore, with the present embodiment, allocation information isallocated to a specific search space shifted based on the CFI value.

This will be explained below in detail. Here, as shown in FIG. 11, thesearch space used in the case of CFI=3 is the same as the search spaceshown in FIG. 8 of Embodiment 2. In this case, as shown in FIG. 11, thetotal number of CCEs N_(CCE)(3)=32 holds. Also, assume that the startinglocation of the search space is n_(CCE4)(3)=8 in the case where the CCEaggregation size is 4, the starting location of the search space isn_(CCE2)(3)=16 in the case where the CCE aggregation size is 2 and thestarting location of the search space is n_(CCE1)(3)=22 in the casewhere the CCE aggregation size is 1, and these values are broadcasted inadvance from a base station to mobile stations.

CCE allocating section 104 calculates the search space in CFI=i (i=1, 2,3) and changes the definition of the search space based on the followingequations.n _(CCE4)(i)=n _(CCE4)(3)−N _(CCE)(3)+N _(CCE)(i)n _(CCE2)(i)=n _(CCE2)(3)−N _(CCE)(3)+N _(CCE)(i)n _(CCE1)(i)=n _(CCE1)(3)−N _(CCE)(3)+N _(CCE)(i)

Here, if the calculation result is negative, the starting location ofthat search space is CCE #0. In the right member of the above equations,the second term and the third term represent the difference between thetotal number of CCEs in the subframe of CFI=3 and the total number ofCCEs in the subframe of CFI=i. That is, the starting location of thesearch space matching each CCE aggregation size in the case of CFI=i isshifted forward by the difference of the total number of CCEs from thestarting location of the search space matching each aggregation size inthe case of CFI=3.

For example, in the case of the subframe of CFI=2, the total number ofCCEs N_(CCE)(2)=24 holds, and therefore CCE allocating section 104defines search spaces based on the above equations. To be more specific,the starting location of the search space matching each CCE aggregationsize is calculated as follows.n _(CCE4)(2)=n _(CCE4)(3)−N _(CCE)(3)+N _(CCE)(2)=0n _(CCE2)(2)=n _(CCE2)(3)−N _(CCE)(3)+N _(CCE)(2)=8n _(CCE1)(2)=n _(CCE1)(3)−N _(CCE)(3)+N _(CCE)(2)=14

Therefore, CCE allocating section 104 defines the search spaces shown inFIG. 12. That is, the search space matching each CCE aggregation size inthe case of CFI=2 is acquired by shifting the CCE numbers by eight CCEs,which are the difference between the total number of CCEs in the case ofCFI=3 (N_(CCE)(3)=32) and the total number of CCEs in the case of CFI=2(N_(CCE)(2)=24). That is, in CCE allocating section 104, the searchspaces are shifted based on the CFI value. Similarly, by calculating theCCE number corresponding to the starting location of the search spacematching each aggregation size in the case of CFI=1 (i.e. the totalnumber of CCEs N_(CCE)(1)=14), CCE allocating section 104 can acquirethe search spaces shown in FIG. 13. Here, in FIG. 13, upon calculatingthe starting locations n_(CCE4)(1) and n_(CCE2)(1) of the search spacesmatching the cases of CCE aggregation sizes of 4 and 2, the calculationresults are negative, and therefore the starting locations aren_(CCE4)(1)=n_(CCE2)(1)=0.

Also, in the same way as in CCE allocating section 104, deciding section210 (in FIG. 2) of mobile station 200 performs blind detection of onlythe allocation information allocated to a specific search space shiftedbased on the CFI value notified from base station 100, for decidingwhether or not that allocation information is the allocation informationdirected to that mobile station. That is, even if CFI varies, it ispossible to find a common definition of search spaces between CCEallocating section 104 of base station 100 and deciding section 210 ofmobile station 200.

Thus, according to the present embodiment, even if the CFI value varies,mobile stations can change the definition of search spaces using thedefinition of search spaces broadcasted from a base station to themobile stations. By this means, it is possible to form optimal searchspaces based on the CFI value without increasing the overhead due tofurther notification information. Therefore, according to the presentembodiment, even if CFI varies, it is possible to acquire the sameeffect as in Embodiment 1.

Embodiment 5

A case will be explained with the present embodiment where CCEs andPUCCHs are associated.

Upon associating CCEs and PUCCHs, a mobile station decides a PUCCHassociated with the lowest CCE number among one or a plurality of CCEsforming the PDCCH to which allocation information for that mobilestation is mapped, as the PUCCH for that mobile station. Therefore, ifall CCEs are associated with PUCCHs on a one-to-one basis, a PUCCH thatis not actually used is found upon CCE aggregation, and, consequently,resource use efficiency degrades. For example, if CCE #0 to CCE #3 arethe CCEs associated with physical resources to which allocationinformation for the subject mobile station is mapped, the mobile stationdecides PUCCH #0 associated with CCE #0 of the lowest number among CCE#0 to CCE #3, as the PUCCH for that mobile station. That is, threePUCCHs from PUCCH #1 to PUCCH #3 other than the PUCCH for the subjectmobile station are not used and are wasted.

Therefore, for example, if the search spaces shown in FIG. 11 ofEmbodiment 4 are defined, with respect to a plurality of CCEs formingthe PDCCH belonging to each search space, a mobile station associatesone PUCCH with the number of CCEs matching the CCE aggregation size. Forexample, one PUCCH is associated with eight CCEs with respect to aplurality of CCEs forming a PDCCH of a CCE aggregation size of 8, andone PUCCH is associated with four CCEs with respect to a plurality ofCCEs forming a PDCCH of a CCE aggregation size of 4. That is, withrespect to a plurality of CCEs forming a PDCCH of a CCE aggregation sizeof n, one PUCCH is associated with n CCEs.

However, as described in Embodiment 4, if the CFI value varies persubframe, the range of the search space matching each CCE aggregationsize is shifted. By this means, the CCEs forming the PDCCH of each CCEaggregation size vary based on the CFI value, and therefore PUCCHsassociated with the CCEs forming the PDCCH of each CCE aggregation sizevary. That is, if the CFI value varies, the association between CCEs andPUCCHs is not optimum.

Also, if the association between CCEs and PUCCH resources is notifiedfrom a base station to a mobile station every time the CFI value varies,the overhead due to notification information increases.

Therefore, based on the association between CCEs in which downlinkallocation information is included and specific PUCCH resources to whicha response signal to downlink data is allocated, where the associationvaries based on the CFI value, the present embodiment controlsblock-wise spreading code sequences and the cyclic shift values of ZACsequences for that response signal.

Among a plurality of PUCCH's, deciding section 210 of mobile station 200(in FIG. 2) according to the present embodiment decides a specific PUCCHto which a response signal to downlink data is allocated, based on CCEsthat are occupied by PDCCHs allocated to a specific search spacematching the CCE aggregation size of the PDCCH to which allocationinformation for that mobile station is allocated, among a plurality ofsearch spaces that vary depending on the CFI value as in Embodiment 4.

Control section 211 controls block-wise spreading code sequences and thecyclic shift values of ZAC sequences for a response signal, based on theassociation between the specific PUCCH decided in deciding section 210,the cyclic shift value of the ZAC sequence and the block-wise spreadingcode sequence, where the association varies depending on the CFI value.

This will be explained in detail. The present embodiment uses the samesearch spaces as in FIG. 11 (CFI=3), FIG. 12 (CFI=2) and FIG. 13 (CFI=3)in Embodiment 4. Also, as in Embodiment 4, base station 100 broadcastssearch space information (n_(CCE4)(3)=8, n_(CCE2)(3)=16, n_(CCE1)(3)=22)to mobile station 200.

Among a plurality of PUCCHs, control section 211 reserves a PUCCHresource associated with the lowest CCE number occupied by a PDCCH ofthe smallest CCE aggregation size.

First, the case of CFI=3 will be explained. Among CCE #0 to CCE #31(CFI=3) shown in FIG. 11, in CCE #0 to CCE #7 immediately before thestarting location n_(CCE4)(3)=8 (CCE #8) of the search space matchingthe case of a CCE aggregation size of 4, one PUCCH resource isassociated with CCE #0 of the lowest number among the CCEs formingPDCCHs.

Next, as shown in FIG. 11, in CCE #8 to CCE #15 between the startinglocation n_(CCE4)(3)=8 (CCE #8) of the search space matching the case ofa CCE aggregation size of 4 and the starting location n_(CCE2)(3)=16(CCE #16) of the search space matching the case of a CCE aggregationsize of 2, two PUCCH resources are associated with the CCEs of thelowest numbers CCE #8 and CCE #12 forming two PDCCHs of a CCEaggregation size of 4 that is the smallest CCE aggregation size.

Similarly, as shown in FIG. 11, in CCE #16 to CCE #21 between thestarting location n_(CCE2)(3)=16 (CCE #16) of the search space matchingthe case of a CCE aggregation size of 2 and the starting locationn_(CCE1)(3)=22 (CCE #22) of the search space matching the case of a CCEaggregation size of 1, three PUCCH resources are associated with theCCEs of the lowest numbers CCE #16, CCE #18 and CCE #20 forming threePDCCHs of a CCE aggregation size of 2 that is the smallest CCEaggregation size.

Similarly, as shown in FIG. 11, in CCE #22 to CCE #31 greater than thestarting location n_(CCE1)(3)=22 (CCE #22) of the search space matchingthe case of a CCE aggregation size of 1, ten PUCCH resources areassociated with CCE #22 to CCE #31 forming ten PDCCHs of a CCEaggregation size of 1.

That is, in the field below the starting location n_(CCE4)(i) of thefield corresponding to the CCEs of CFI=i, one PUCCH resource isassociated with eight CCEs. Also, in the field equal to or above thestarting location n_(CCE4)(i) and below the starting locationn_(CCE2)(i), one PUCCH resource is associated with four CCEs. Similarly,in the field equal to or above the starting location n_(CCE2)(i) andbelow the starting location n_(CCE1)(i), one PUCCH resource isassociated with two CCEs. Also, in the field above the starting locationn_(CCE1)(i), one PUCCH resource is associated with one CCE.

Thus, based on search space information broadcasted from base station100, control section 211 controls PUCCH resources for a response signalaccording to the association between CCEs and PUCCH resources, where theassociation varies depending on the CFI value.

Here, as shown in FIG. 14, assume that the priority order regarding ause of physical resources associated with PUCCHs (i.e. the use order ofsequence numbers) is notified in advance from a base station to a mobilestation. Here, a physical resource (i.e. PUCCH resource) of a lowerPUCCH number is preferentially associated with a CCE. In the associationshown in FIG. 14, PUCCH numbers are defined by the cyclic shift values(0 to 11) of ZAC sequences and the sequence numbers (0 to 2) ofblock-wise spreading code sequences. In this case, PUCCH resourcesassociated with CCEs are as shown in FIG. 15. To be more specific, asshown in FIG. 15, the PUCCH number associated with CCE #0 is defined byZAC sequence #0 and block wise spreading code sequence #0, and the PUCCHnumber associated with CCE #8 is defined by ZAC sequence #0 andblock-wise spreading code sequence #2. Also, the present invention isnot limited to these sequence lengths.

Next, the association between CCEs and PUCCH resources in CFI=2 will beexplained.

In the same way as in CFI=3, control section 211 associates a PUCCHresource and the CCE lowest number occupied by the PDCCH of the smallestCCE aggregation size in the search space of CFI=2 among a plurality ofPUCCHs.

That is, in the case of CFI=2, as shown in FIG. 12, PUCCH resources areassociated with the CCEs of the lowest numbers CCE #0 and CCE #4 formingthe PDCCHs of a CCE aggregation size of 4 among CCE #0 to CCE #7, PUCCHresources are associated with the CCEs of the lowest numbers CCE #8, CCE#10 and CCE #12 forming the PDCCHs of a CCE aggregation size of 2 amongCCE #8 to CCE #13, and PUCCH resources are associated with CCE #14 toCCE #23 forming PDCCHs of a CCE aggregation size of 1 among CCE #14 toCCE #23.

In this case, PUCCH resources associated with CCE numbers are as shownin FIG. 16. Here, comparing associated PUCCH resources in CFI=3 (in FIG.15) and associated PUCCH resources in CFI=2 (in FIG. 16), the associatedPUCCH resources in CFI=2 shown in FIG. 16 are reduced. Further, theassociated CCE numbers are different between the PUCCH resources shownin FIG. 15 and the PUCCH resources shown in FIG. 16.

Thus, according to the present embodiment, even if the CFI value varies,by using search space information broadcasted from a base station, amobile station can associate CCEs and PUCCHs based on search spaces thatvary depending on the CFI value. Further, even if the CFI value varies,by reserving only the minimum PUCCH resources, it is possible to preparesufficient resources for transmitting response signals.

Also, in the same way as in the case of CFI=1, as shown in FIG. 17,control section 211 updates the association between CCEs and PUCCHs.

Thus, according to the present embodiment, based on search spaceinformation (about the starting location of the search space matchingeach CCE aggregation size) in the specific CFI value, a mobile stationcan associate CCEs and PUCCH resources according to the change of theCFI value. Therefore, according to the present embodiment, even if theCFI value varies, by optimally associating CCEs and PUCCH resourcesaccording to the definition of search spaces that varies depending onCFI and reserving only the minimum PUCCH resources, it is possible toprepare sufficient resources for transmitting response signals withoutnotifying, from a base station to mobile stations, the associationbetween CCEs and PUCCH resources every time the CFI value varies.

Also, although a case has been described above with the presentembodiment where PUCCH resources are defined based on the associationbetween ZAC sequences and block-wise spreading code sequence shown inFIG. 15, FIG. 16 and FIG. 17, the present invention is not limited tothe association between ZAC sequences and block-wise spreading codesequence shown in FIG. 15, FIG. 16 and FIG. 17.

Also, as PUCCH resources, it is possible to use resources other than thecyclic shift values of ZAC sequences and block-wise spreading codesequences. For example, resources that are separated by frequencies suchas subcarriers and resources that are separated by time such as SC-FDMAsymbols are possible.

Embodiments of the present invention have been described above.

Also, the total number of CCEs that can be used per subframe (i.e. thetotal number of CCEs that can be present in one subframe) in the aboveembodiments varies depending on the system bandwidth, the number of OFDMsymbols that can be used as CCEs, and the total number of controlsignals (e.g. ACK/NACK to uplink data) that are not used to notifyresource allocation results of downlink/uplink data.

Also, a PUCCH used for explanation in the above embodiments is thechannel for feeding back an ACK or NACK, and therefore may be referredto as an “ACK/NACK channel.”

Also, although cases have been described above with embodiments whereCCEs and PUCCHs (i.e. response signals to downlink data) are associated,the present invention can acquire the same effect as above byassociating CCEs and PHICHs (Physical Hybrid ARQ Indicator CHannels).Here, response signals to uplink data are allocated to the PHICHs.

Also, even in the case of using the search spaces shown in FIG. 18, itis possible to implement the present invention in the same way as above.FIG. 18 shows grouping a plurality of mobile stations and using thesearch spaces that are used per group and the search spaces that areused per CCE aggregation size. Thus, even in the case of distributing aplurality of CCEs to a plurality of mobile station groups and applyingthe present invention to each group, it is possible to acquire the sameeffect as above. Also, even in the case of using the definition ofsearch spaces shown in FIG. 19, it is possible to implement the presentinvention in the same way as above. As shown in FIG. 19, a configurationis employed where the search spaces matching respective CCE aggregationsizes do not overlap. By this means, different search spaces do notoverlap, so that it is possible to acquire the same effect as above andreduce the resources to reserve for PUCCH resources.

Also, even in the case of feeding back control information other thanresponse signals, it is possible to implement the present invention inthe same way as above.

Also, a mobile station may be referred to as a “terminal station,” “UE,”“MT,” “MS” or “STA (STAtion)”. Also, a base station may be referred toas “Node B,” “BS” or “AP.” Also, a subcarrier may be referred to as a“tone.” Also, a CP may be referred to as a “GI (Guard Interval)”. Also,a CCE number may be referred to as a “CCE index.”

Also, the error detecting method is not limited to CRC check.

Also, a method of performing conversion between the frequency domain andthe time domain is not limited to IFFT and FFT.

Also, although a case has been described above with the embodimentswhere signals are transmitted using OFDM as a downlink transmissionscheme and SC-FDMA as an uplink transmission scheme, the presentinvention is equally applicable to the case where transmission schemesother than OFDM and SC-FDMA are used.

Although a case has been described with the above embodiments as anexample where the present invention is implemented with hardware, thepresent invention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSIs, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSIs as aresult of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

The invention claimed is:
 1. A base station apparatus comprising: circuitry, which, in operation, allocates a control information to one or more consecutive control channel elements (CCEs) in a search space, the search space being comprised of a plurality of CCEs that includes the one or more consecutive CCEs, the plurality of CCEs starting on a CCE that is determined from both a number of the one or more consecutive CCEs, and a total number of CCEs configured in a subframe, and a CCE index of a first CCE of the one or more consecutive CCEs being associated with an uplink resource; and a transmitter, which, in operation, transmits the allocated control information to a mobile station.
 2. The base station apparatus according to claim 1, wherein said transmitter, in operation, transmits downlink data on a downlink resource that is indicated by the control information, and the uplink resource is used for transmitting an ACK or NACK for the downlink data from the mobile station.
 3. The base station apparatus according to claim 1, wherein the search space is comprised of the plurality of CCEs that are specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 4. The base station apparatus according to claim 1, wherein the search space is comprised of the plurality of CCEs, and a number of the plurality of CCEs is specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 5. The base station apparatus according to claim 1, wherein the plurality of CCEs starts on a CCE that is specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 6. The base station apparatus according to claim 1, wherein the CCE, on which the plurality of CCEs starts, is different between the numbers of the one or more consecutive CCEs.
 7. The base station apparatus according to claim 1, wherein the CCE, on which the plurality of CCEs starts, is a CCE having a minimum CCE number among CCE numbers of the plurality of CCEs.
 8. The base station apparatus according to claim 1, wherein said transmitter, in operation, transmits a control format indicator (CFI), and the total number of CCEs configured in a subframe is obtained based on a value of the CFI.
 9. A communication method comprising: allocating a control information to one or more consecutive control channel elements (CCEs) in a search space, the search space being comprised of a plurality of CCEs that includes the one or more consecutive CCEs, the plurality of CCEs starting on a CCE that is determined from both a number of the one or more consecutive CCEs, and a total number of CCEs configured in a subframe, and a CCE index of a first CCE of the one or more consecutive CCEs being associated with an uplink resource; and transmitting the allocated control information to a mobile station.
 10. The communication method according to claim 9, comprising transmitting downlink data on a downlink resource that is indicated by the control information, and the uplink resource is used for transmitting an ACK or NACK for the downlink data from the mobile station.
 11. The communication method according to claim 9, wherein the search space is comprised of the plurality of CCEs that are specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 12. The communication method according to claim 9, wherein the search space is comprised of the plurality of CCEs, and a number of the plurality of CCEs is specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 13. The communication method according to claim 9, wherein the plurality of CCEs starts on a CCE that is specific to both the number of the one or more consecutive CCEs and the total number of CCEs configured in a subframe.
 14. The communication method according to claim 9, wherein the CCE, on which the plurality of CCEs starts, is different between the numbers of the one or more consecutive CCEs.
 15. The communication method according to claim 9, wherein the CCE, on which the plurality of CCEs starts, is a CCE having a minimum CCE number among CCE numbers of the plurality of CCEs.
 16. The communication method according to claim 9, comprising transmitting a control format indicator (CFI), and the total number of CCEs configured in a subframe is obtained based on a value of the CFI. 